Ethology 094\ 292*205 "0888# Þ 0888 Blackwell Wissenschafts!Verlag\ Berlin ISSN 9068Ð0502

Communication Biolo`y Research Group\ Department of Zoolo`y\ University of the Witwatersrand\ Johannesbur` and CNRS URA 556\ Laboratoire d|Etholo`ie Experimentale et Comparee\ Universite Paris Nord\ Villetaneuse

Fecundity and the Behavioural Pro_le of Reproductive Workers in the Queenless \ Pachycondyla " Ophthalmopone# berthoudi

Matthew F[ Sledge\ Christian Peeters + Robin M[ Crewe

Sledge\ M[ F[\ Peeters\ C[ + Crewe\ R[ M[ 0888] Fecundity and the behavioural pro_le of reproductive workers in the queenless ant\ Pachycondyla " Ophthalmopone# berthoudi[ Ethology 094\ 292*205[

Abstract Morphologically specialized queens are absent in Pachycondyla " Ophthal! mopone# berthoudi "ant subfamily #[ Instead\ several of the workers mate and reproduce "gamergates#[ Gamergate proportion in nests commonly varies between nests and di}erent times of the year[ Individual fecundity of gamergates varies according to the number of these individuals in a nest\ and we examined their behaviour in relation to fecundity in nests with di}erent proportions of gamergates[ In nests with high proportions of gamergates\ they exhibited a diversity of behaviours inside the nest and in some cases could not be distinguished behav! iourally from sterile workers[ The fecundity of these gamergates was low and variable[ In nests with low proportions\ gamergates were relatively more fecund\ and did not participate in colony labour[ The behavioural pro_le of gamergates is therefore linked to their reproductive physiology\ which is in~uenced by the number of mated individuals in the nest[ Corresponding author] M[ F[ Sledge\ Dipartimento di Biologia Animale e Genetica\ UniversitaÁ di Firenze\ Via Romana 06\ I!49014\ Florence\ Italy[ E!mail] msledgeÝdbag[uni_[it

Introduction Division of colony labour has been proposed as one of the major reasons for the considerable ecological success of social "Oster + Wilson 0867^ HoÃlldo! bler + Wilson 0889^ Bourke + Franks 0884#[ The simultaneous performance of di}erent tasks by colony members serves to enhance the e.ciency with which the environment is exploited for colony growth and maintenance[ In many this is further enhanced by morphological specialization[ Queens possess enlarged abdomens and ovaries for egg production\ while sterile workers are specialized

U[ S[ Copyright Clearance Center Code Statement] 9068!0502:88:0943Ð9292,03[99:9 293 M[ F[ Sledge\ C[ Peeters + R[ M[ Crewe "reduced ovaries and a simpli_ed thorax# for performing tasks related to colony growth and development "foraging\ brood care\ and defence#\ and engage in little\ if any\ reproduction[ In most ants division of labour within the worker caste is based on temporal changes in task performance\ where workers specialize on particular tasks "e[g[ defence or brood care# for prolonged periods of time "Oster + Wilson 0867^ HoÃlldobler + Wilson 0889#[ Recently\ though\ alternative views have been proposed as to how labour is organized in social societies "Deneu! bourg et al[ 0876^ Tofts + Franks 0881^ Traniello + Rosengaus 0886^ Franks et al[ 0886#[ There may even be further specialization within the worker caste\ where workers are physically adapted to performing certain behaviours\ and several size classes of workers may occur "HoÃlldobler + Wilson 0889#[ This latter phenomenon is noticeably absent in all but one species of the ant subfamily Ponerinae "Me`a! ponera foetens^ Wilson 0842^ Longhurst + Howse 0868^ Villet 0889a#[ As in other ants\ colony labour in ponerine ants is performed by functional groups of indi! viduals specialized in the di}erent tasks required within the society\ with two to _ve categories of workers usually de_ned "Villet 0889a\b#[ This has been dem! onstrated in several species\ such as Pachycondyla apicalis "Fresneau + Dupuy 0877#\ Pachycondyla caffraria "Agbogba + Howse 0881#\ and Ponera pennsyl! vannica "Pratt et al[ 0883#[ The subfamily Ponerinae is of further interest because of the existence of ¼ 099 species in which the queen caste is absent "Peeters 0880\ 0882#[ Studies on such species are of interest because they approximate an ancestral condition and o}er valuable information on the factors that a}ect social evolution in many other [ In these ants\ mated egg!laying workers "gamergates# have replaced queens as the functional reproductives\ with either monogyny "single gamergate# or poly! gyny "multiple gamergates# described in di}erent species[ Division of labour in queenless ants is similar to that of those ants with queens[ Colony labour is performed by functional groups of sterile workers\ and there is a clear pattern of temporal polyethism "Peeters 0886#[ In polygynous queenless ants the in~uence of the level of reproductive activity on the behavioural pro_les of reproductive wor! kers has not previously been investigated[ In monogynous species\ gamergates have a behavioural pro_le distinct from that of sterile workers as they generally perform fewer behaviours than sterile workers and are never active outside the nest "Ware et al[ 0889^ Villet 0880a\b\ 0881#[ Furthermore\ in some species gamergates can be distinguished by the performance of unique behaviours\ e[g[ egg or brood care "Villet 0880b\ 0881#[ In this study we investigated the relationship between gamergate ovarian activity and behaviour in the queenless\ polygynous ponerine ant Pachycondyla " Ophthalmopone# berthoudi[ As a result of di}erences in male success at _nding nests during the limited period of male activity "Jan[ to Mar[#\ nests contain varying proportions of gamergates "2Ð52) of individuals# "Peeters + Crewe 0874#[ Furthermore\ the proportion of gamergates decreases within nests after the mating period due to an increase in the number of sterile workers\ colony _ssion events\ redistribution of individuals to other nests\ or gamergate death[ We have docu! mented that in P[ berthoudi individual gamergate fecundity varies according to the Fecundity and Behaviour in a Queenless Ant 294 number of gamergates in a nest "Sledge et al[ 0885#[ As this reproductive e}ect is expected to in~uence the way in which labour is organized in the colony\ we assessed the e}ects of variation in fecundity on gamergate behavioural pro_les in nests with di}erent proportions of gamergates[ Methods Seven nests of P[ berthoudi were collected over a 1 yr period from Dunstable Farm "29>49? E\ 14>14? S# in the Northern Province of South Africa[ The colonies were maintained in modi_ed Lubbock nests placed in large wooden arenas[ Tem! perature and humidity were maintained at 14Ð29>C and 49Ð69)\ respectively[ Workers were individually colour!coded using Tippexþ correcting ~uid[ Colonies of this ant are polydomous "one to seven nests per colony#\ and thus the terms {colony| and {nest| are used here with distinctly di}erent meanings[ Scan samples "n  49# of instantaneous behaviours performed by each ant were collected from each nest in order to group individuals performing similar behav! iours[ Nest observations spanned either 19 or 15 d[ The results were analysed using the centroid!linkage hierarchical cluster analysis of Systat 4[91 and Statistica 3[4 for Windows[ The groups resulting from the cluster analyses were characterized in the following way] similar behaviours were grouped and their frequencies summed and divided by the number of workers in the colony[ This resulted in a colony! average frequency for each set of behaviours[ The frequency with which a particular group of workers performed a speci_c set of behaviours was then compared with the colony average\ and this was used to determine the best set of behaviours characterizing the group[ This method\ together with cluster analysis\ has illustrated the distinct behavioural pro_les of gamergates in other studies "Fresneau + Dupuy 0877^ Villet 0880a\b\ 0881#[ A similar agglomeration level was chosen delimiting groups in each of the nests[ This choice was arbitrary\ but was made to be as biologically meaningful as possible in that we felt it approximated existing groups within each nest[ As gamergates cannot be recognized visually\ the ovaries of all workers were dissected on completion of behavioural observations to determine reproductive status[ Gamergates are recognized by the presence of sperm in the spermatheca "sperm reservoir# and the presence of developing oocytes in the ovaries[ The following features were recorded in order to assess the fecundity of individual gamergates] 0[ the number of yolk!containing mature "with a chorion and at least the size of a newly laid egg# and immature oocytes^ and 1[ the presence of large\ dark yellow bodies "corpora lutea# at the base of individual ovarioles[ These are formed by the remains of nurse and follicular cells when eggs are laid\ and indicate the level of past egg laying by an individual[ Egg resorption does not occur in P[ berthoudi[ Results Reproductive Status of Workers Table 0 presents the demographic data of the seven study nests and the results of dissections of workers[ Gamergate number ranged from one "0[5) of nest R# 295 M[ F[ Sledge\ C[ Peeters + R[ M[ Crewe

Table 0] Nest composition and reproductive status of workers in seven nests of Pachycondyla berthoudi[ Nest O was the only nest that was collected with males

Mean "SD# Mean "SD# no[ of Nest Date of Workers Workers No[ of no[ of mature immature code collection collected dissected gamergates oocytes oocytes

A 08 Mar[ 0883 24 24 5 9[55 "9[36# 0[55 "9[36# B 06 Mar[ 0883 40 40 02 9[50 "9[37# 0[42 "9[73# O 08 Mar[ 0884 007 098 5 0[22 "9[36# 1[55 "0[09# N1 08 Mar[ 0884 034 097 1 1[4 "9[4# 3 "9# P 15 Mar[ 0885 058 036 35 9[04 "9[24# 0[97 "9[42# Q 16 Mar[ 0885 70 58 01 9[30 "9[38# 0[30 "9[75# R 16 Mar[ 0885 58 48 0 2 0

to 35 "16) of nest P#[ In those nests containing more than 09) gamergates\ less than one mature oocyte occurred on average[ Gamergates in nests A\ B\ P\ and Q lacked yellow bodies in their ovaries\ suggesting that they had only recently commenced egg laying[ In the remaining nests "N1\ O\ and R# all gamergates possessed one or more mature oocytes and large\ dark yellow bodies[ No virgin workers had developed ovaries in any of the study nests[

Division of Labour and the Behaviour of Gamergates Between 14 "nest B# and 17 "nest A# distinct behaviours were observed for both virgin workers and gamergates[ Resting was the most frequent behaviour "Table 1\ Figs 0Ð3#[ Interactions between workers were restricted to grooming and reciprocal antennation[ Trophallaxis was never seen\ but the mandibles of foragers returning from outside were often investigated "with the antennae# by workers within the nest[ Workers of P[ berthoudi specialize either in work inside or outside the nest "Figs 0Ð3#[ Cluster analyses of scan samples and combined sociograms of nests A and O "six gamergates each#\ P "35 gamergates# and R "one gamergate# "Figs 0Ð3# are presented[ At an arbitrarily assigned agglomeration level "the same in each nest#\ seven groups are de_ned in nest A "Fig[ 0#\ four in nest O "Fig[ 1#\ three in nest P "Fig[ 2#\ and two in nest R "Fig[ 3#[ In nest A a further subdivision of worker groups remaining in the nest is evident[ Group G "Fig[ 0# performed higher than average levels of resting\ while group F "Fig[ 0# was concerned mainly with brood care[ In this nest various single workers were separated by cluster analysis on the basis of high performances of usually one task "e[g[ C\ E\ and A\ Fig[ 0#[ In nest O\ two heterogeneous groups of workers performed much of the labour in the nest\ including brood care and domestic activities "groups C and D\ Fig[ 1#\ while group A was active outside the nest[ Similar results were obtained for the other nests "Figs 2\ 3#[ Fecundity and Behaviour in a Queenless Ant 296 9[90 Ð After mating activity Prior to mating Nests A\ B\ P and Q contained recently mated gamergates with ÐÐÐÐ ÐÐ ÐÐÐÐÐ ABQPR ON1 Nest Nest Nest Nest Nest Nest Nest Pachycondyla berthoudi[ No[ of gamergates 5 02 01 35 0 5 1 by any gamergates was not observed during sampling[ Furthermore\ gamergates were never active outside the nests Ethograms for gamergates in seven nests of Behaviour Proportion of gamergates 06) 14) 04) 16) 0) 4) 0) Rest insideWalk insideRest alert "inside nest#Groom selfBe groomedReciprocal antennationInspect eggsCarry eggsInspect larvaeRest near larvaeCarry larvaeGroom larvae 9[95 9[30 9[92 9[95 9[92 9[31 9[90 9[91 9[954 9[96 Ð 9[614 9[93 9[92 9[931 Ð Ð 9[608 9[91 9[09 9[90 9[94 9[93 9[924 Ð 9[992 9[77 9[90 9[901 9[09 9[97 9[904 Ð 9[95 Ð 9[993 Ð 9[991 9[904 9[94 9[92 9[991 9[72 Ð 9[996 9[992 9[924 9[906 9[991 Ð 9[93 9[91 9[992 9[76 9[91 9[91 9[904 Ð Ð 9[92 ! Ð 9[90 Ð 9[93 Ð 9[90 Ð Ð Ð Ð 9[90 Ð Ð Ð Ð 9[92 Rest near cocoon"s#Inspect cocoonCarry cocoonFeed on termitesGuard nestLook out nestInspect nestInspect foodMark nestNest maintenanceGroom workerInspect worker 9[92 Ð Ð 9[90 9[92 9[911 9[95 9[91 Ð 9[90 9[95 9[93 9[90 9[997 9[991 9[90 9[91 Ð Ð Ð 9[91 9[91 9[995 9[97 9[90 9[991 9[991 Ð 9[991 9[92 Ð 9[994 Ð 9[90 Ð 9[991 Ð Ð 9[998 Ð Ð Ð 9[992 Ð Ð Ð Ð Ð Ð Ð 9[909 Ð 9[931 Ð Ð 9[993 Ð Ð 9[906 9[90 Ð Ð Ð 9[93 Ð Ð 9[95 Ð Ð Ð Ð Ð Ð Ð Ð Ð Ð Ð low fecundities "one or nowere mature also oocytes\ very see fecund Table "one 0#\ or while the more single mature gamergate oocytes# in and nest possessed R large\ was dark very yellow fecund[ bodies\ In indicating nests a O history and of N1 gamergates egg laying[ Oviposition Table 1] 297 M[ F[ Sledge\ C[ Peeters + R[ M[ Crewe

Fig[ 0] Combined dendrogram and sociogram of nest A "six gamergates\ 24 workers in total# generated by hierarchical cluster analysis[ Workers are grouped according to frequencies of behaviours performed[ Gamergates are numbered 0Ð5[ The dotted line indicates the arbitrary descriptive level determining seven groups of workers "AÐG#[ The white parts of the his! tograms show the level of specialization for a particular task for each individual worker[ No particular behaviour distinguishes gamergates from nonreproductive workers[ The behaviours that were performed most frequently were regrouped into the following cate! gories] OA\ activities outside nest^ RI\ immobile inside nest^ D\ domestic activities "e[g[ nest inspection and maintenance#^ EC\ carrying of eggs^ LC\ carrying and grooming of larvae^ CC\ carrying of cocoons Fecundity and Behaviour in a Queenless Ant 298

Fig[ 1] Combined dendrogram and sociogram of nest O "six gamergates\ 098 workers in total#[ Six gamergates were present in the nest and are clustered together in a single group "indicated by the asterisk#[ They are distinguished from nonreproductive workers by the high levels of resting that they exhibited[ Colony labour is performed by three groups of workers[ Behavioural categories as in Fig[ 0

Distinct di}erences in the frequencies of task performance by gamergates were observed between the nests with high proportions of gamergates "and low 209 M[ F[ Sledge\ C[ Peeters + R[ M[ Crewe

Fig[ 2] Combined dendrogram and sociogram of nest R "one gamergate\ 48 workers in total# of Pachycondyla berthoudi[ The gamergate is distinguished from nonreproductive workers by the high levels of resting that it exhibited[ The asterisk indicates the gamergate[ Behavioural categories as in Fig[ 0

fecundity# "nests A\ B\ P\ Q# and those with low proportions "and high fecundity# "nests O\ N1 and R#[ In the former nests\ gamergates participated in some form of Fecundity and Behaviour in a Queenless Ant 200

Fig[ 3] Combined dendrogram and sociogram of nest P "35 gamergates\ 036 workers in total# of Pachycondyla berthoudi[ No particular behaviour distinguishes gamergates from nonreproductive workers[ Gamergates performed most\ or all\ of the range of behaviours seen[ Similar results were obtained for those nests with high proportions of gamergates with low fecundities[ Asterisks indicate gamergates[ Behavioural categories as in Fig[ 0 201 M[ F[ Sledge\ C[ Peeters + R[ M[ Crewe colony labour\ performing behaviours at varying frequencies "Table 1#[ This is best illustrated when nests A and O are compared "Table 1\ Figs 0\ 1#[ Both these nests contained six gamergates\ but this constituted 06) of nest A and only 4) of nest O[ Furthermore\ gamergates in nest O were more fecund than those in nest A as they had well developed ovaries and large yellow bodies "Table 1#[ In nest A\ three gamergates exhibited higher than average levels of resting inside the nest\ while two others performed brood care at relatively high frequencies[ The remaining gamergate performed mostly domestic activities[ In contrast\ gamergates in nest O were observed to rest most of the time and little\ if any\ contribution was made to colony labour "Table 1\ Fig[ 1#[ An analysis of task performance in this nest clus! tered the gamergates together on the basis of high frequencies of resting inside the nest "Fig[ 1#[ Similar results were obtained when nests P and R were compared[ Despite being collected after the mating period\ nest R contained only a single gamergate\ making up 0[5) of the total nest population[ This individual was highly fecund with two mature oocytes and large\ dark yellow bodies\ and performed behaviours with similar frequencies to those of gamergates in nests O and N1 "Table 1\ Fig[ 2#[ In contrast\ in nest P "also collected after mating activity#\ gamergates constituted 16) of the nest population\ and were behaviourally variable\ participating in colony labour "Fig[ 3#[ These individuals possessed much lower fecundities "never more than one mature oocyte#\ and also lacked yellow bodies at the base of the ovarioles[

Discussion Colony!level division of labour in P[ berthoudi does not di}er fundamentally from the patterns described in other ponerine ants "reviewed by Peeters "0886##[ Nests showed a marked division of the workforce into workers con_ned inside the nest and workers that spent the majority of their time outside the nest[ Further subdivisions of workers into more discrete roles\ such as nest guarding and brood care\ may be based on restriction of each task to di}erent parts of the nest[ Similar patterns have been described for monogynous\ queenless species\ such as Platythyrea schultzei "Villet 0880b#\ P[ cf[ cribrinodis "Villet 0880a#\ P[ lamellosa "Villet et al[ 0889#\ Pachycondyla kru`eri "Villet + Wildman 0880#\ and the poly! gynous species Lepto`enys schwabi "Davies et al[ 0883#[ The results of an earlier study show that gamergates are more fecund in nests with low gamergate numbers "Sledge et al[ 0885#\ while we show here that the percentage of mated individuals in a nest\ their fecundity and behavioural pro_le are correlated in P[ berthoudi[ What is the nature of the link between fecundity and the behavioural pro_les of gamergates< Nests A\ B\ P and Q had high proportions of gamergates with low fecundities and no yellow bodies in their ovaries[ These gamergates performed the same behaviours as nonreproductive workers "with the exception of foraging#\ although brood care and resting were mostly observed[ In contrast\ in nests O\ N1 and R\ gamergates did not contribute to colony labour\ resting for more than 79) of the time[ These individuals possessed well!developed Fecundity and Behaviour in a Queenless Ant 202 ovaries[ This variation in gamergate behaviour could be attributed to di}erences in their ovarian activity\ although it is likely that there are other factors involved[ As there is no social control over which workers mate "although only young workers are attractive to males#\ when a large proportion of workers mate in a nest\ gamergate fecundity is expected to be low initially[ As gamergate number "and proportion# decreases after the mating period\ fecundity of individual gamer! gates will increase "Sledge et al[ 0885#[ Surviving gamergates are thus expected to perform less labour as the year progresses\ displaying a more restricted behavioural pro_le as their fecundity increases "as seen in nests O and N1#[ In a similar manner\ if very few workers are mated\ this results in gamergates being more fecund "as in nest R#\ and they will not perform any labour[ This may account for the di}erences between nests A and O in this study[ Both these nests contained six gamergates\ constituting 06) of nest A and only 4) of nest O[ Nest A was collected after the mating period and\ thus\ had been recently visited by males\ while nest O was collected before male activity "Peeters + Crewe 0875# and had been reproductively active for longer[ Factors such as work load and the length of time since mating events also a}ect gamergate fecundity[ Similarly\ in some social wasps\ as queens acquire helpers after nest initiation "either subordinates or worker o}spring#\ they give up tasks such as defence and foraging\ and only perform reproductive duties "Jeanne 0880#[ In P[ berthoudi\ the labour requirements of a particular nest may initially inhibit ovary development in recently mated workers\ and as time since mating "and virgin worker proportion# increases\ the inhibitory e}ects of work load will decrease[ Furthermore\ the development of the ovaries will initiate a switch in behavioural pro_le from that characteristic of sterile workers to that of mature gamergates[ Nests collected in Mar[ may therefore contain recently mated workers whose behavioural pro_les are becoming biased towards reproductive duties[ This is to be expected as they were collected after the period of male activity "Jan[ to Mar[# "Peeters + Crewe 0875#[ The relationship between division of labour and ovary development in repro! ductive individuals appears to be a general phenomenon in many polygynous ants "HoÃlldobler + Wilson 0889#[ In the ponerine species\ Odontomachus rixosus\ the behaviour of queens is correlated with the number of developed oocytes in their ovaries "Ito et al[ 0885#[ Similarly\ in Ectatomma tuberculatum behavioural di}er! ences between workers have been shown to be related to di}erences in ovarian development "Feneron et al[ 0885#[ In contrast\ in monogynous species such as Me`aponera foetens "Villet 0889a# and Ponera pennsylvanica "Pratt et al[ 0883# the highly fecund queens perform no colony labour at all[ In other ant subfamilies\ queens\ as a result of a large degree of morphological specialization\ also do not participate in colony labour and perform only reproductive duties "HoÃlldobler + Wilson 0889#[ For example\ in Zacryptocerus varians and Colobopsis sp[ "subfamily Formicinae#\ and Leptothorax acervorum "subfamily Myrmicinae# the behaviour of queens is restricted to self!grooming and trophallaxis with workers "Cole 0879^ Bourke 0880#[ In some social wasps "which lack dimorphic queens and workers#\ queens perform no work at all during the colony cycle "Jeanne 0879#[ 203 M[ F[ Sledge\ C[ Peeters + R[ M[ Crewe Behavioural ~exibility and variation in role specialization is a widespread feature of eusocial insects "Gordon 0885#[ Workers can revert to other activities if the need arises\ allowing for colony stability in the face of unpredictable environ! mental change "Robinson 0881^ Bourke + Franks 0884#[ As a result of small colony size\ individual variability is more conspicuous in ponerine ants "e[g[ Lachaud + Fresneau 0876^ Corbara et al[ 0878#\ minimizing the e}ects of disruptions in colony labour[ Thus\ it may be adaptive for gamergates in P[ berthoudi to engage in nonreproductive labour because the absence of regulation at the mating stage can result in large proportions of mated workers[ In order to maintain a viable colony\ gamergates must contribute to colony maintenance activities until a new cohort of sterile workers has been produced[ Gamergates may be biased to performing {worker!like| behaviours when gamergate proportion is high "and\ thus\ individual fecundity low\ as a result of mutual regulation^ Sledge et al[ 0885# following the mating period[ As new workers are reared and the gamergate number decreases\ gamergates progressively reduce behaviours that are directed to colony main! tenance and display the limited behavioural pro_le of highly fecund individuals[ This ultimately ensures that the e.cient organization of labour in individual nests is maintained when gamergate proportion is high[ The compositions of the nests recorded in Table 0 are a re~ection of the particular historical circumstances that preceded their collection[ Factors that a}ect the composition are] 0[ the number of nests of which the colony is composed^ 1[ the number of individuals in the nest^ 2[ the proportion of the nest that is made up of reproductives^ 3[ the degree to which individuals move from nest to nest within a colony\ and the degree to which reproductives are actively redistributed between nests^ and 4[ the time since males visited a nest and produced gamergates by inseminating virgin workers[ The particular combination of these factors that have had an impact on a nest will then determine the rate at which gamergates undergo changes in their behavioural pro_les[ This is a complex function of ovarial development modulated by particular within!nest conditions[ The behavioural ~exibility required of individual P[ berthoudi workers by their complex colony organization has been exempli_ed by this study of their behaviour[

Acknowledgements

We would like to thank Luc Passera and Ed Vargo for their input\ and Graham Alexander\ Rob Brooks\ Dominique Fresneau\ JuÃrgen Liebig\ and Tish Silberbauer and an anonymous referee for reviewing the manuscript[ Thanks are also extended to Mervyn Mason for help with collection of the colonies\ Theresa Wossler for her technical assistance\ the Mitchell family for use of their farm to collect the colonies\ and Hamish Robertson "South African Museum\ Cape Town# for con_rming the identi_cation of the ants[ Financial assistance was provided by the Communication Biology Research Group of the University of the Witwatersrand and the Foundation for Research Development[

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Traniello\ J[ F[ A[ + Rosengaus\ R[ B[ 0886] Ecology\ evolution and division of labour in social insects[ Anim[ Behav[ 42\ 198*102[ Villet\ M[ H[ 0889a] Division of labour in the Matabele ant Me`aponera foetens "Fabr[# "Hymenoptera\ Formicidae#[ Ethol[ Ecol[ Evol[ 1\ 286*306[ Villet\ M[ H[ 0889b] Social organization of Platythyrea lamellosa "Roger# "Hymenoptera] Formicidae# II[ Division of labour[ S[ Afr[ J[ Zool[ 14\ 143*158[ Villet\ M[ H[ 0880a] Reproduction and division of labour in Platythyrea cf[ cribrinodis "Gerstaecker 0747# "Hymenoptera] Formicidae#] comparisons of individuals\ colonies and species[ Trop[ Zool[ 3\ 198*120[ Villet\ M[ H[ 0880b] Social di}erentiation and division of labour in the queenless ant Platythyrea schultzei Forel 0809 "Hymenoptera] Formicidae#[ Trop[ Zool[ 3\ 02*18[ Villet\ M[ H[ 0881a] The social biology of Ha`ensia havilandi "Forel 0890# "Hymenoptera] Formicidae#\ and the origin of queenlessness in ponerine ants[ Trop[ Zool[ 4\ 084*195[ Villet\ M[ H[\ Hart\ A[ + Crewe\ R[ M[ 0889] Social organization of Platythyrea lamellosa "Roger# "Hymenoptera] Formicidae#] I[ Reproduction[ S[ Afr[ J[ Zool[ 14\ 149*142[ Villet\ M[ H[ + Wildman\ M[ H[ 0880] Division of labour in the obligately queenless ant Pachycondyla " Bothroponera# kruÃ`eri Forel 0809 "Hymenoptera Formicidae#[ Trop[ Zool[ 3\ 122*149[ Ware\ A[ B[\ Compton\ S[ G[ + Robertson\ H[ G[ 0889] Gamergate reproduction in the ant Stre! blo`nathus aethiopicus Smith "Hymenoptera] Formicidae] Ponerinae#[ Insectes Soc[ 26\ 078*088[ Wilson\ E[ O[ 0842] The origin and evolution of polymorphism in ants[ Quart[ Rev[ Biol[ 17\ 025*045[

Received] May 5\ 0887

Initial acceptance] June 11\ 0887

Final acceptance] October 12\ 0887 "W[ Wickler#